Plasma diagnosis system using multiple-reciprocating-path thompson scattering

ABSTRACT

Provided is a plasma diagnosis system using multiple-reciprocating-path Thompson scattering. The plasma diagnosis system includes: alight source which supplies pulsed laser beams; an optical system which sequentially supplies a pulsed laser beam in a vertical polarization state and a pulsed laser beam in a horizontal polarization state; a collection optic system which measures a first collection signal scattered from the plasma when the pulsed laser beam in the vertical polarization state is focused and measures a second collection signal scattered from the plasma when the pulsed laser beam in the horizontal polarization state is focused; and a controller which measures a Thomson scattering signal for the plasma by using the first and second collection signals measured by the collection optic system, and the second collection signal is a background scattering noise signal.

TECHNICAL FIELD

The present invention relates to a plasma diagnosis system using Thomsonscattering, and more particularly, a plasma diagnosis system usingmultiple-reciprocating-path Thompson scattering capable of measuring anaccurate Thomson scattering signal by measuring a Thomson scatteringsignal and a background scattering noise signal in plasma by using anoptical system configured to rotate polarization by 90 degrees accordingto the number of times of reciprocating propagation and removing thebackground scattering noise signal.

BACKGROUND ART

In tokamak-type nuclear fusion, typically, deuterium atoms and tritiumatoms are heated up to so high temperature to generate a plasma state inwhich ionized atomic nuclei and electrons have free mobility, and theplasma is confined by using a strong toroidal magnetic field, so thatthe nuclei overcome Coulomb force and come close enough to cause fusionreaction at sufficiently high temperature. In order to stably operateand control this high-temperature, high-density plasma state, it isnecessary to know the temperature and density of the plasma, and thus,accurate measurement thereof is required. As a result of this request,various types of plasma diagnosis apparatuses have been developed andused. As one of the plasma diagnosis apparatuses, there is a diagnosisapparatus using Thomson scattering, which is an essential diagnosisapparatus for measuring temperature and density of electrons.

FIG. 1 is a configuration diagram schematically illustrating a diagnosisapparatus using Thompson scattering in the related art for diagnosing astate of plasma in a tokamak of a nuclear fusion reactor.

Referring to FIG. 1, a diagnosis apparatus 1 using Thomson scattering inthe related art for diagnosing a state of plasma in a tokamak 5 of anuclear fusion reactor includes a light source which outputs a strongpulsed laser beam polarized in a vertical direction, an optical system110 which focuses the laser beam in the vertical polarization state intoa plasma in the TOKAMAK, a laser beam dump 120 which is mounted outsidethe tokamak and absorbs and removes the laser beam emitted from thetokamak, and a collection optic system 130 which collects the lightscattered by the laser beam.

More specifically, in order to measure the temperature and density ofelectrons in the plasma, the above-described diagnosis apparatus 1 usingThomson scattering focuses a laser pulse with a single wavelength (1064nm) having a strong electric field intensity from the outside of thetokamak 5 into the plasma-filled tokamak by using the light source 100and the optical system 110. The nuclei and electrons constituting theplasma are vibrated in the polarization direction of the electric fieldof the laser beam according to a temporal change of the strongunidirectional electric field strength (polarized light) of the focusedlaser beam, and a light beam with the same frequency as the incidentlaser beam is emitted and is subjected to Thompson scattering. In thiscase, the light is not subjected to Thomson scattering in the directionparallel to the polarization direction of the laser beam. Therefore, inthe case where the polarization of the laser beam incident on the crosssection of the tokamak in FIG. 1 is perpendicular to this cross section,scattered light is emitted in the direction of collection optic system,so that the scattered light can be received by the collection opticsystem. On the contrary, in the case where the laser beam ishorizontally polarized with respect to the cross section of tokamak inFIG. 1, no Thomson scattered light is emitted toward the collectionoptic system, so that there is no Thomson scattered light received bythe collection optic system.

On the other hand, since the plasmas are moving fast, the scatteredlight has a Doppler shift in wavelength due to the Doppler effect.Therefore, the diagnosis apparatus using Thomson scattering can acquirethe temperature of electrons in the plasma by measuring the wavelengthshift due to the Doppler effect and can also acquire the density ofelectrons according to the intensity of light to be measured. That is,if signals of the Thomson scattered light in the plasma are accuratelymeasured, the temperature and density of the plasma can be accuratelyacquired.

However, there exist the light beams that are reflected by incompleteoptical parts to be incident on the tokamak and the light beams that arescattered multiple times by wall surfaces of the tokamak and the like,and these light beams are called stray light.

As the background noise caused by the stray light is included in theThomson scattering signal measured by the diagnosis apparatus usingThomson scattering in the related art, there is a problem in that theaccuracy of the measured Thompson scattering signal is lowered.

SUMMARY OF THE INVENTION Technical Problem

In order to solve the problems described above, the present invention isto provide a plasma diagnosis system using a multiple-reciprocating-pathThompson scattering system capable of measuring an accurate Thomsonscattering signal from which a background scattering noise signal isremoved by using an optical system.

Solution to Problems

According to an aspect of the present invention, there is provided aplasma diagnosis system using Thomson scattering, including: a lightsource which supplies pulsed laser beams having predeterminedpolarization and wavelength; an optical system which sequentiallysupplies a pulsed laser beam in a vertical polarization state and apulsed laser beam in a horizontal polarization state by using the pulsedlaser beams supplied from the light source; a collection optic systemwhich measures a first collection signal scattered from the plasma whenthe pulsed laser beam in the vertical polarization state supplied fromthe optical system is focused and measures a second collection signalscattered from the plasma when the pulsed laser beam in the horizontalpolarization state supplied from the optical system is focused; and acontroller which measures a Thomson scattering signal for the plasma byusing the first and second collection signals measured by the collectionoptic system, wherein the first collection signal is a signal in which aThomson scattering signal and a background scattering noise signal aremixed, and the second collection signal is a background scattering noisesignal.

Preferably, in the plasma diagnosis system using Thomson scatteringaccording to the above aspect, the optical system may include: apolarizing beam splitter which is disposed on an optical path of thepulsed laser beam supplied from the light source; a first reflectingmirror which supplies the pulsed laser beams reflected from thepolarizing beam splitter back to the polarizing beam splitter; a Faradayrotator which is disposed on the optical path of the pulsed laser beampassing through the polarizing beam splitter and rotates thepolarization state by 45 degrees and outputs the pulsed laser beam; afocusing lens which focuses the pulsed laser beam supplied from theFaraday rotator on the plasma; and a second reflecting mirror whichreflects and supplies the focused pulsed laser beam back to the focusinglens, and the pulsed laser beam in the vertical polarization state andthe pulsed laser beam in the horizontal polarization state may besequentially supplied to the plasma.

Preferably, in the plasma diagnosis system using Thomson scatteringaccording to the above aspect, the Thomson signals measured during thetime when the vertically polarized pulses are reciprocated may besynchronized and added, so that it is possible to improve asignal-to-noise ratio.

Preferably, in the plasma diagnosis system using Thomson scatteringaccording to the above aspect, a half wave plate may be disposed betweenthe light source and the optical system.

Preferably, the plasma diagnosis system using Thomson scatteringaccording to the above aspect, may further include a trigger modulewhich generates and outputs trigger signals when the pulsed laser beamsin the horizontal polarization state and the pulsed laser beams in thevertical polarization state are supplied from the optical system,respectively, wherein the collection optic system is driven according tothe trigger signals output from the trigger module,

More preferably, the trigger module may be disposed between the lightsource and the optical system or at an arbitrary position of the opticalsystem and generates and outputs the trigger signal when detecting thatthe pulsed laser beam is supplied from the light source to the opticalsystem, detecting that the pulsed laser beam is supplied from theoptical system to the plasma, or detecting that the pulsed laser beam issupplied at an arbitrary position of the optical system.

Preferably, the plasma diagnosis system using Thomson scatteringaccording to the above aspect may be applied to a tokamak-type nuclearfusion reactor, wherein he optical system focuses a pulsed laser beaminto a tokamak, the collection optic system collects scattered opticalsignals in the tokamak and measures the scattered optical signals foreach wavelength band by using a polychrometer, and the controllermeasures and supplies a Thomson scattering signal in the tokamak.

Effects of the Invention

The multiple-path plasma diagnosis system according to the presentinvention sequentially supplies a pulsed laser beam in a verticalpolarization state and a pulsed laser beam in a horizontal polarizationstate to a tokamak to be focused through multiple reciprocating paths,so that it is possible to measure and supply a Thomson scattering signalfrom which a background scattering noise signal is removed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram schematically illustrating a diagnosisapparatus using single-path Thompson scattering in the related art fordiagnosing a state of plasma in a tokamak of a nuclear fusion reactor.

FIG. 2 is a configuration diagram schematically illustrating a plasmadiagnosis system using multiple-reciprocating-path Thomson scatteringaccording to a preferred embodiment of the present invention.

FIG. 3 is a diagram illustrating a polarization state of a pulsed laserbeam in each stage in the plasma diagnosis system usingmultiple-reciprocating-path Thomson scattering according to thepreferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In a plasma diagnosis system using Thomson scattering according to thepresent invention, a pulsed laser beam in a vertical polarization stateand a pulsed laser beam in a horizontal polarization state aresequentially supplied into a tokamak in a nuclear fusion reactor throughmultiple reciprocating paths, and scattering signals in the tokamak aremeasured, so that it is possible to accurately measure a Thomsonscattering signal from which a background scattering noise signal isremoved.

Hereinafter, a structure and operation of a plasma diagnosis systemusing Thompson scattering according to a preferred embodiment of the present invention will be described in detail with reference to theaccompanying drawings.

FIG. 2 is a block diagram schematically illustrating a plasma diagnosissystem using multiple-reciprocating-path Thompson scattering accordingto a preferred embodiment of the present invention.

Referring to FIG. 2, a plasma diagnosis system 2 according to thepresent invention is installed outside a tokamak 5 of a nuclear fusionreactor and includes a light source 200, an optical system 220 whichsequentially supplies a vertically-polarized pulsed laser beam and ahorizontally-polarized pulsed laser bam to the tokamak, a collectionoptic system 230 which collects scattered light in the tokamak, atrigger module 240, and a controller 250.

The light source 200 outputs a pulsed laser beam in a horizontalpolarization state with a single wavelength of 1064 nm and a strongelectric field intensity.

The first half wave plate (HWP) 214 is disposed on the optical path ofthe pulsed laser beam output from the light source to select andmaintain the polarization state of the propagating pulsed laser beam.

The optical system 220 is provided between the light source and thetokamak 5 to sequentially supply a pulsed laser beam in a verticalpolarization state and a pulsed laser beam in a horizontal polarizationstate to the tokamak.

The optical system 220 includes a polarizing beam splitter (PBS) 221disposed on the optical path of the pulsed laser beam supplied from thelight source, a Faraday rotator (FR) 222, a second half wave plate (HWP)224, and a focusing lens 226 disposed on the optical path of the pulsedlaser beam passing through the PBS, a second reflecting mirror 227 forreflecting the beam focused by the focusing lens 226 and supplying thebeam back to the focusing lens, and a first reflecting mirror 229disposed on a reflecting path of the PBS.

The second reflecting mirror uses a concave lens to focus the beam backto the position of Thompson scattering, and the first reflecting mirroruses a convex lens to collimate the reflected light.

The polarizing beam splitter (PBS) 221 transmits the beam in thehorizontal polarization state and reflects the beam in the verticalpolarization state.

The Faraday rotator 222, the second half wave plate 224, and thefocusing lens 226 are sequentially disposed on the optical path of thepulsed laser beam passing through the PBS 220. The Faraday rotator 222rotates the polarization state of the pulsed laser beam passing throughthe PBS 221 by 45 degrees and outputs the pulsed laser beam, and thesecond half wave plate 224 rotates the beam output from the Faradayrotator 222 by 45 degrees, so that the pulsed laser beams in thehorizontal polarization state are in the vertical polarization state bythe Faraday rotator 222 and the second half wave plate 224. The firsthalf wave plate 214 may be omitted in the case where the polarizationfrom the laser beam source is in a perfectly horizontal polarizationstate. In some cases, in principle, the second half wave plate 224 maybe omitted according to the position of a Thomson scattering collectionunit. The focusing lens 226 focuses the pulsed laser beam in thevertical polarization state on a predetermined position in the tokamakin the nuclear fusion reactor. When the pulsed laser beam is focusedinto the tokamak by the focusing lens, the first Thomson scattering isstrongly generated in the direction of the collection optic system. As aresult, the first-1 collection signal, in which the backgroundscattering noise signal and the Thomson scattering signal are mixed iscollected by the collection optic system 230 and is transmitted to apolychrometer, by which the collection signal is is measured for eachwavelength band.

The second reflecting mirror 227 may be installed inside or outside thetokamak and reflects the beam passing through the tokamak back to thefocusing lens. In this stage, the collection optic system measures thefirst-2 collection signal in which the background scattering noisesignal and the Thomson scattering signal are mixed.

The first reflecting mirror 229 is disposed in the reflecting path ofthe PBS 221. The pulsed laser beam in the vertical polarization statereflected from the PBS propagates to be reflected by the firstreflecting mirror 229 and is incident on the PBS again.

The optical system 220 having the above-described configurationsequentially supplies the pulsed laser beam in the vertical polarizationstate and the pulsed laser beam in the horizontal polarization stateinto the tokamak in the nuclear fusion reactor.

The collection optic system 230 collects the beam scattered from thetokamak to measure the intensity of the beam. The collection opticsystem collects the beams according to the trigger signal of the triggermodule and supplies collection signals to the controller.

The trigger module 240 generates the trigger signals and outputs thetrigger signals to the collection optic system and/or the controllerwhen the pulsed laser beam in the horizontal polarization state and thepulsed laser beam in the vertical polarization state are supplied fromthe optical system. The trigger module may detect an extra laser beamsignal transmitted through a folding mirror disposed at a trigger pointset between the light source and the optical system or at an arbitraryposition of the optical system to use the extra laser beam signal as atrigger signal.

The collection optic system is driven according to the trigger signaloutput from the trigger module to collect light scattered in the tokamakand supply the scattered light.

The controller 250 measures a Thomson scattering signal with nobackground scattering noise signal by using the first and secondcollection signals supplied from the collection optic system andsupplies the Thomson scattering signal. More specifically, thecontroller allows Thomson scattering to be generated from the plasma inthe tokamak by the pulsed laser beam in the vertical polarization stateof the optical system and measures the first collection signal in whichthe Thomson scattering signal and the background scattering noise signalare mixed. In addition, the controller allows Thomson scattering not tobe generated from the plasma in the tokamak by the pulsed laser beam inthe horizontal polarization state of the optical system and measures thesecond collection signal configured with only the background scatteringnoise signal. Therefore, the controller can accurately measure only thepure Thomson scattering signal by removing the second collection signalconfigured with only the background scattering noise signal from thefirst collection signal in which the Thomson scattering signal and thebackground scattering noise signal are mixed.

Hereinafter, the operation of the plasma diagnosis system usingmultiple-reciprocating-path Thompson scattering having theabove-described configuration according to the preferred embodiment ofthe present invention will be described in detail with reference to FIG.3.

FIG. 3 is a diagram illustrating a polarization state of the pulsedlaser beam in each stage in the plasma diagnosis system usingmultiple-reciprocating-path Thompson scattering according to thepreferred embodiment of the present invention.

Referring to FIG. 3, when a pulsed laser beam in a horizontalpolarization state is output and supplied from the light source, in thefirst forward stage, the pulsed laser beam passes through the PBS 221,passes through the FR 222 to be rotated by 45 degrees, and is rotated by45 degrees again by the second HWP 224, so that the pulsed laser beam isconverted to be in the vertical polarization state. When the pulsedlaser beam in the vertical polarization state is focused on apredetermined position inside the tokamak, the first Thomson scatteringis strongly generated in the direction of the collection optic system230. As a result, the collection optic system measures the first-1collection signal in which the background scattering noise signal andthe Thomson scattering signal are mixed.

Next, the beam focused into the tokamak propagates after Thompsonscattering and is reflected by the second reflecting mirror 227, and thefirst backward stage proceeds. In the first backward stage, as thepulsed laser beam is focused into the tokamak, the second Thomsonscattering is generated. The collection optic system measures the secondfirst-2 collection signal in which the background scattering noisesignal and the Thomson scattering signal are mixed due to the secondThompson scattering.

Next, in the first backward stage, the pulsed laser beam in the verticalpolarization state passing through the tokamak passes through the secondHWP 224 and is rotated by 45 degrees in the backward direction by 45degrees, and returns to the original state and as the beam is rotated by45 degrees by the FR 222 again, so that the pulsed laser beam is in thevertical polarization state.

The pulsed laser beam in the vertical polarization state is reflected bythe PBS 221 and propagates to the first reflecting mirror 229.

The pulsed laser beam in the vertical polarization state reflected bythe first reflecting mirror is incident on the PBS 221 again and thenreflected.

Next, in the second forward stage, the pulsed laser beam in the verticalpolarization state incident on the PBS from the first reflecting mirroris reflected by the PBS, passes through the FR 222, and is rotated by 45degrees. The pulsed laser beam is converted to be in the horizontalpolarization state by the second HWP 224.

As the pulsed laser beam in the horizontal polarization state is focusedinside the tokamak, Thomson scattering is not generated in the directionof the collection optic system 230, and the collection optic systemmeasures the second-1 collection signal configured with only thebackground scattering noise signal.

Next, the beam focused into the tokamak propagates and is reflected bythe second reflecting mirror 227, and the second backward stageproceeds. In the second backward stage, the pulsed laser beam in thehorizontal polarization state are focused again inside the tokamak andpropagate to the focusing lens with no Thomson scattering in thedirection of the collection optic system 230. At this time, thecollection optic system measures the second-2 collection signalconfigured with only the background scattering noise signal.

The controller receives the first-1 and first-2 collection signals inwhich the background scattering noise signal and the Thomson scatteringsignal are mixed from the collection optic system and receives thesecond-1 and second-2 collection signals configured with only thebackground scattering noise signal, so that it is possible to accuratelymeasure only the Thomson scattering signal by using these collectionsignals.

As described above, the plasma diagnosis system using themultiple-reciprocating-path Thomson scattering according to the presentinvention can accurately measure the Thomson scattering signal.

On the other hand, the plasma diagnosis system according to the presentinvention can be applied to a tokamak-type nuclear fusion reactor. Inthis case, the optical system focuses the pulsed laser beams into thetokamak, the collection optic system collects scattered optical signalsin the tokamak, and the controller measures the Thomson scatteringsignal in the tokamak.

While the present invention has been particularly illustrated anddescribed with reference to exemplary embodiments thereof, it should beunderstood by the skilled in the art that the invention is not limitedto the disclosed embodiments, but various modifications and applicationsnot illustrated in the above description can be made without departingfrom the spirit of the invention. In addition, differences relating tothe modifications and applications should be construed as being includedwithin the scope of the invention as set forth in the appended claims.

INDUSTRIAL APPLICABILITY

The plasma diagnosis system according to the present invention can beused variously in apparatuses requiring measurement of the temperatureand density of plasma, and in particular, can be used to diagnose thestate of plasma inside a tokamak-type nuclear fusion reactor.

1. A plasma diagnosis system using multiple-reciprocating-path Thomsonscattering, comprising: a light source which supplies pulsed laser beamshaving predetermined polarization and wavelength; an optical systemwhich sequentially supplies a pulsed laser beam in a verticalpolarization state and a pulsed laser beam in a horizontal polarizationstate by using the pulsed laser beams supplied from the light source; acollection optic system which measures a first collection signalscattered from the plasma when the pulsed laser beam in the verticalpolarization state supplied from the optical system is focused andmeasures a second collection signal scattered from the plasma when thepulsed laser beam in the horizontal polarization state supplied from theoptical system is focused; and a controller which measures a Thomsonscattering signal for the plasma by using the first and secondcollection signals measured by the collection optic system, wherein thefirst collection signal is a signal in which a Thomson scattering signaland a background scattering noise signal are mixed, and the secondcollection signal is a background scattering noise signal.
 2. The plasmadiagnosis system according to claim 1, wherein the optical systemincludes: a polarizing beam splitter (PBS) which is disposed on anoptical path of the pulsed laser beam supplied from the light source; afirst reflecting mirror which supplies the pulsed laser beams reflectedfrom the PBS back to the PBS; a Faraday rotator which is disposed on theoptical path of the pulsed laser beam passing through the PBS androtates the polarization state by 45 degrees and outputs the pulsedlaser beam; a focusing lens which focuses the pulsed laser beam suppliedfrom the Faraday rotator on the plasma; and a second reflecting mirrorwhich reflects and supplies the focused pulsed laser beam back to thefocusing lens, and wherein the pulsed laser beam in the verticalpolarization state and the pulsed laser beam in the horizontalpolarization state are sequentially supplied to the plasma.
 3. Theplasma diagnosis system according to claim 1, further comprising anoptical isolator between the light source and the optical system, andwherein the optical isolator causes the pulsed laser beam supplied fromthe light source to propagate to the optical system but prevents thebeam output from the optical system from entering the light source. 4.The plasma diagnosis system according to claim 1, further comprising atrigger module which generates and outputs trigger signals when thepulsed laser beams in the horizontal polarization state and the pulsedlaser beams in the vertical polarization state are supplied from theoptical system, respectively, wherein the collection optic system isdriven according to the trigger signals output from the trigger module.5. The plasma diagnosis system according to claim 4, wherein the triggermodule is disposed between the light source and the optical system or atan arbitrary position of the optical system and generates and outputsthe trigger signal when detecting that the pulsed laser beam is suppliedfrom the light source to the optical system, detecting that the pulsedlaser beam is supplied from the optical system to the plasma, ordetecting that the pulsed laser beam is supplied at an arbitraryposition of the optical system.
 6. The plasma diagnosis system accordingto claim 1, wherein the optical system focuses the pulsed laser beaminto the plasma, the collection optic system collects and measuresscattered optical signals in the plasma, and the controller measures andsupplies the Thomson scattering signal in the plasma.
 7. The plasmadiagnosis system according to claim 1, being applied to a plasmaapparatus in which temperature and density of electrons are required tobe measured.